1. Field of the Invention
The present invention relates to a vehicle door latch device which has an improved door-holding force for keeping a door in a closed position against a strong external force applied to the door by an automobile accident or the like.
2. Prior Art
As shown in FIGS. 7 and 8, a conventional door latch device has a housing A with a space fixed to one of a vehicle door and a vehicle body, a U-shaped striker B fixed to the other of the door and the vehicle body, a latch D rotatably mounted in the space by a latch shaft C and being engageable with the striker B, and a ratchet E rotatably mounted in the space and being engageable with the latch D for holding the engagement between the latch D and the striker B. The housing A has a base F which contains a parallel plate G substantially parallel to a rotational plane of the latch D, and an approach path H formed on the parallel plate G for receiving the striker B when the door is closed.
The strength or door-holding force of the latch device essentially depends on thickness of each of the latch D and the base F, and a diameter of the latch shaft C.
FIG. 8 shows test results obtained by applying a large load to the conventional latch device. As can be clearly seen from FIG. 8, when the striker B is strongly pulled by the large load in the direction of an arrow J parallel to an axis of the latch shaft C, the latch D and the plate G of the base F are bent, and the striker B is then disengaged from the latch D, thereby the door is open.